value, notifies the 3270 display system
that
the next byte in
the data stream
is
an attribute character.
For
a description
of
how the 3270 display system uses attribute characters,
and to determine the values to specify for attribute
characters and the start-field order, see the
IBM
3270
Information Display System Component Description.
After processing DIAGNOSE code
X'58',
CP
sets a
condition code.
If
the operation was successful -
that
is, no
110
errors occurred -
CP
sets a condition code
of
zero.
If
an
110
error occurred, CP sets a condition code
of
one.
If
an
I/O
error occurred, the application program can check
the
I/O
status and the error type by:
• Issuing a TEST
I/O
(TIO) instruction
• Examining the returned condition code
Examining the virtual CSW
The returned condition codes and CSW status are the
standard condition codes and status defined in
the
IBM
Systeml370
Principles
of
Operation.
You must also make sure that the interrupt for
the
virtual
device
is
enabled by setting the appropriate bit
and
channel
mask in the PSW.
For
example, if the virtual address
of
your
console
is
OIF, bit 0 in the channel mask must
be
set to one
(that is, bit
0 must be on). This may be
the
case if you are
loading programs in the
VM/PC
CMS transient area.
Full Screen Mode
DIAGNOSE
X'58'
provides a means by which a virtual
machine may share, with CP, control
of
a 3270 display
station. Two
CCW
operations,
X'29'
and
X'2A',
in addition
to performing the requested
I/O,
notify
CP
that
the
display
station
is
operating under the control of the virtual machine.
CCW
code
X'29'
performs a WRITE,
or
ERASE/WRITE,
operation, depending
on
the value of the control field.
For
the WRITE, and
ERASE/WRITE,
the virtual machine must
provide appropriate control information beginning with the
A-22
VM/PC
Users Guide
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